Food-collecting and waste-rejecting mechanisms in Glottidia pyramidata and the persistence of lingulacean inarticulate brachiopods in the fossil record

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Abstract
Potentially inedible particles entering the mantle cavity of Glottidia pyramidata impinge on the frontal surfaces of ungrooved outer tentacles and are removed very efficiently by frontal cilia beating directly towards the exhalent aperture. Particles which settle out of the inhalent current are resuspended by cilia on the mantle ampullae. Edible material passing between the outer tentacles is captured by the combined action of laterofrontal cilia beating into the grooves and frontal cilia beating towards the bases of the inner grooved tentacles of the spirolophous lophophore. The arrangement of the tentacles and their cilia on the spirolophe of G. pyramidata is contrasted with the plectolophous condition in the articulate brachiopod Laqueus californianus in which heavy potentially inedible particles penetrate deeply into the lophophore before being trapped by ungrooved tentacles which, because of differences between the developmental patterns of articulates and inarticulates, lie within the grooved tentacles. Furthermore, the immobile laterofrontal cilia on both sets of tentacles of L. californianus detect waste particles. It is suggested that the exterior position of the waste-rejecting tentacles and the involvement of the laterofrontal cilia in food collection in lingulacean inarticulates may have contributed to their ability to compete successfully with bivalve molluscs in turbid habitats and their persistence in the fossil record.